Various embodiments of the present invention relate to an assembly and method for slipforming a slot drain with concrete. The assembly includes a slipform paver, a movable sleeve adapted to fit over a void forming means, a first taut tether, sensing means and one or more actuators. The first taut tether is provided and maintained in an inclined or declined disposition to provide a parallel reference for guiding the sleeve which in use is driven forward by the slipform paver. The sensing means are adapted to receive guidance from the inclined or declined tether for dictating the elevations and dispositions of the sleeve. The one or more actuators are connected to the sleeve and adapted to be controlled by the sensing means to achieve the dictated elevations and dispositions of the sleeve.